A star polymer is a copolymer consisting of a core part and arm parts having polymer chains extended from the core part. Various star polymers have conventionally been developed, but those star polymers with practically suitable physical properties particularly as resist materials have not yet been developed.
On the other hand, among star polymers, examples of the star polymers using a styrene-based polymer as the arm parts include those star polymers described in the following documents.
In Patent Documents 1 and 2, an alkenylphenol-based homopolymer or copolymer is used as the arm parts and a polyfunctional coupling agent is used as the core part which couples the arm part polymers. As the polyfunctional coupling agent, the documents exemplify an aromatic compound such as a divinyl aromatic compound and a trivinyl aromatic compound, diepoxide, diketone, dialdehyde, and a compound represented by general formula (CR1R2X)nR3 (wherein X represents a substituent selected from the group consisting of a halogen atom, alkoxy group having 1-6 carbons and acyloxyl group having 2-6 carbons. R1 and R2 respectively represent a hydrogen atom or a monovalent hydrocarbon group having 1-6 carbons, where R1 and R2 may be the same or different. R3 represents a polyvalent aromatic hydrocarbon group or polyvalent aliphatic hydrocarbon group that may have n (CR1R2X) substituents. n represents any integer from 3 to 6).
Further, Patent Document 3 describes using a copolymer of an alkenylphenol derivative and a (meth)acrylate derivative as the arm parts, and using as the core part a polymer chain consisting of the repetition units induced by diacrylate represented by the following formula
(wherein R4 and R8 each independently represent a hydrogen atom or a methyl group, R5, R6, R9 and R10 each independently represent an alkyl group, and R7 represents an alkylene group), and that the core part is bound to polymers of the arm parts.
Still further, Patent Document 4 describes a dendrimer-like star polymer, and describes reacting a compound which has a functional group reactable with anion and which serves as a core part with arm parts which consist of polymers comprising styrene-based repetition units and which are polymer chains having 2 or more anionic ends. As the compound which has a functional group reactable with anion and which serves as a core part, the Patent Document 4 exemplifies chain or cyclic aliphatic, aromatic and heterocyclic compounds and describes that an aromatic compound is particularly preferred.